Electric gaseous discharge tubes



Feb. 17, 1959. G.F. KLEPP l E .TA L 2,87

' ELECTRIC GASEOUS DISCHARGE TUBES Filed M 17, 19s: 2 Sheets-Sheet 1 Gasff/ling 94% 99 neon nema/nden Argon, pressure 20-25 mm Hg (zero zemenature cqefflc/bnt of main aining voltage) Inventor GE KLEPP- DMILLER Afforney Feb. 17, 1959 G. F. KLEPP' ET AL 2,37

- ELECTRIC GASEOUS DISCHARGE TUBES Filed July 17, 1953 2 Sheets-Sheet 2PRESSURE H9) 'u (un .0

MA/Nm/N/NC vomcs DIFFZPENCE' woL rs) Inventor GE KLEP .MILLER A Home yUnited States Patent ELEcTRrc GASEOUS DISCHARGE TUBES George FrancisKlepp and Donald Miller, London, England, assignors to InternationalStandard Electric Corporation, New York, N. Y.

. Application July 17, 1953, Serial No. 368,641 Claims priority,application Great Britain July 23, 1952 1 filaim. (Cl. 313-185) Thepresent invention relates to cold cathode gas-filled electric dischargetubes, particularly such as are used to provide a reference voltage instabilised power supplies and the like.

Cold cathode electric glow discharge tubes are characterised in thatwhen once an anode-cathode voltage of sufficient magnitude, dependingupon the gas pressure and the anode-cathode separation, is applied tothe tube, glow discharge occurs and may be maintained at a considerablylower voltage, referred to as the maintaining voltage of the tube. Overa wide range of discharge current the maintaining voltage may vary butslightly, the discharge being said to be norma and being characterisedby. the fact that the cathode glow does not completely cover the wholeof the available cathode surface. At higher discharge currents, when theglow completely covers the cathode, the anode-cathode voltage risesrapidly with increase of current, the discharge being said to beabnormal. For some time past use has been made of this property of thecold cathode discharge tubes to stabilise the output voltage in mainssupply'stabilizers and the like. As implied above, however, themaintaining voltage, even in the region of normal discharge is notentirely independent of current, and a given voltage drop across thetube is obtainable only at a specified value of discharge current. Undersuch limitations, the cold cathode glow discharge tube is widely used asa source of reference voltage. Improvements in tube design have nowreached the point where very stable voltages may be obtained providedthe tube is run in a temperature controlled enclosure, it being foundthat a major source of voltage variation is due to a temperaturecoefiicient of maintaining voltage.

The present applicants have conducted investigations with a view tocontrolling the temperature coeflicient of maintaining voltage in glowdischarge tubes used as sources of reference voltage. They have foundthat the value of this temperature coefficient, with a given gasfilling,may be critically dependent upon the amount of gas present, i. e. uponthe gas pressure.

In accordance with one aspect of the present invention there is provideda cold cathode gas-filled electric discharge tube in which the pressureof the gas-filling is regulated so that under given operating conditionsof normal discharge the temperature coeflicient of anodecathode voltageis substantially zero.

Rather than to make measurements of the actual temperature coefiicientinvolved it has been found that the difierence between the anode-cathodevoltage for a given cathode current immediately after switching on andafter thermal equilibrium has been attained provides a suflicientmeasure of the temperature coeflicient, although "therefore, there isprovided a cold cathode gas-filled electric glow discharge tube in whichthe pressure of the gas-filling is adjusted to a value at which there issubstantially no ditference between the anode-cathode voltage for-agiven cathode current immediately after switching on and after thermalequilibrium between the tube and its surroundings has been attained.

The invention will be more fully described with reference to theaccompanying drawings which show, in Fig. l a particular type of tube,and in Fig. 2 a graph of the variation with pressure of the differencein maintaining voltage immediately after switching on and at a giventime later.

The tube to which the drawing relates was a voltage reference tubehaving an anode and a cathode activated by cerium-mischmetal, the tubegeometry being such that with a gas filling of 97% neon and 3% argonnormal glow discharge was obtained for cathode currents up to 40milliamperes. At a pressure of 30 mm. of mercury and ambient temperatureof 20 C., the tube had a maintaining voltage of 79 volts at 40 macurrent. The temperature coefficient of maintaining voltage, however,was found to be considerable.

Experiments were made with different batches of tube, each batch beingfilled with the same gas and to a difierent press'ure and at the sametemperature. The maintaining voltage was measured at 40 ma. dischargecurrent immediately after establishing glow discharge and again at thesame current, after a lapse of one minute. The variation between tubesof a given batch was very small, but the diiferences between the tworeadings of maintaining voltage varied markedly between difierentbatches and was found to lie on a curve which is re produced in thedrawing. In this graph filling gas pressure in millimeters of mercury at20 C. is plotted against the maintaining voltage difference. It will beseen that below 25 mm. of pressure the voltage diiference is very small,it becomes a negative maximum at 30 mm. pressure, becomes zero again at34 mm. pressure goes to a positive maximum and then returns to zero at38 mm. pressure. Subsidiary tests proved that the actual temperaturecoeflicient of maintaining voltage followed a similar trend to that ofthe voltage difference plotted on the graph, and that the latter,therefore, could be taken as a sufiicient measure of the variation ofthe temperature coefficient.

In the type of tube to which the accompanying graph relates a highdegree of stability of maintaining voltage may be obtained when thefilling pressure lies between 20 and 25 mm. mercury, or is adjusted to34 mm. or to 38 mm. At the latter two points, of course the actualpressure is somewhat more critical. On the other hand, if desired, thefilling pressure may be adjusted to provide some other given positive ornegative temperature coefficient.

Our experiments indicatethat substantially similar qualitative resultsto those describedabove may be obtained when the gas mixture variesbetween 94 and analogous results are to be expected with other gasmixtures.

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What we claim is:

A voltage stabilizer electric discharge tube of the cold cathode typecomprising an envelope containing a gas filling of 97% neon and 3% argonat a pressure of 25:2 millimeters of mercury, an anode and a cathodeactivated with cerium mischmetal said anode spaced it from said cathodea given distance, said distance being such that the anode-cathodemaintaining voltage over a glow discharge current range of 5 ma. to ma.lies between and volts, the variation of voltage with current being lessthan 7 volts.

References Cited in the file of this patent UNITED STATES PATENTS1,749,423 Fenton Mar. 4, 1930 1,834,251 Moore Dec. 1, 1931 1,965,585Foulke July 10, 1934 2,507,696 Depp May 16, 1950 2,728,005 VictoreenDec. 20, 1955

1. A VOLTAGE STABILIZER ELECTRIC DISCHARGE TUBE OF THE COLD CATHODE TYPECOMPRISING AN ENVELOPE CONTAINING A GAS FILLING OF 97% NEON AND 3% ARGONAT A PRESSURE OF 25+2 MILLMETERS OF MERCURY, AN ANODE AND A CATHODEACTIVATED WITH CERIUM MISCHMETAL SAID ANODE SPACED FROM SAID CATHODE AGIVEN DISTANCE, SAID DISTANCE BEING SUCH THAT THE ANODE-CATHODEMAINTAINING VOLTAGE OVER A GLOW DISCHARGE CURRENT RANGE OF 5 MA. TO 40MA. LIES BETWEEN 70 AND 80 VOLTS, THE VARIATION OF VOLTAGE WITH CUARRENTBEING LESS THAN 7 VOLTS.